1. Field of the Invention
The present disclosure generally relates to an image scanning unit for scanning documents.
2. Description of the Background Art
Typically, an image scanning unit employs a document-moving scanner to scan the document and create an image thereof. In such document-moving scanner, a document transported along a contact glass may be scanned by an optical scanning unit, which is fixed at a given position. If foreign matter accumulates on a document scan position of the optical scanning unit, such foreign matter may be scanned as well, and the whole document appear as an abnormal image (e.g., streaked, etc.), thus degrading image quality.
In view of such drawbacks, JP-S62-262563-A discloses an optical scanning unit having a contact-type image sensor, in which a groove is formed at a document scan position of a translucent protective layer of the contact-type image sensor and a document contacts the translucent protective layer. With such a configuration, adhesion of ink on the document to a document scan position of the translucent protective layer can be prevented, and scanned image quality can be enhanced.
Further, JP-2897690-B discloses another image sensor unit in which a document scan surface made of a transparent glass includes a convex portion and a concave groove. The convex portion having a given uniform width extends in a direction perpendicular to a document transport direction, and the concave groove is formed parallel to the convex portion and closer to a document insertion side of the unit. The document is transported from the concave groove to the convex portion on the document scan surface and is scanned when the document passes a flat top of the convex portion.
In the image sensor unit described above, excess ink on the document can be scraped away at a base portion of the concave groove and the convex portion, by which adhesion of ink to a document scan position onto the convex portion can be prevented. With such a configuration, document image may be scanned with higher quality.
However, the above-described methods might have room for improvement. For example, in JP-S62-262563-A, with the groove formed at a scan position, ink or foreign matter (e.g., dust) on the document may be scraped at a corner-portion of the groove and accumulate in the groove, and thereby an abnormal image may occur inadvertently.
In JP-2897690-B, ink or foreign matter (e.g., dust) on the document may be scraped at the base portion of the concave groove and the convex portion, and the top face (or document scan surface) of the convex portion contacts the document in such condition. If foreign matter (e.g., unfixed toner) still adheres to the document, the top face (or document scan surface) of the convex portion may be contaminated by the foreign matter, by which an abnormal image may occur inadvertently.
Such contamination of the document scan surface may be prevented by forming a number of concave grooves therein, but such configuration may not be practical given the cost of manufacture.